CaSR agonists

ABSTRACT

By searching various kinds of compounds having CaSR agonistic activity, the present invention provides CaSR agonistic agents, pharmaceutical compositions, preventive or therapeutic agents for diarrhea and kokumi-imparting agents each of which comprise the compound. More specifically, the present invention provides CaSR agonistic agents, pharmaceutical compositions, preventive or therapeutic agents for diarrhea and kokumi-imparting agents each of which comprise a glutamic acid derivative having CaSR agonistic activity or pharmaceutically acceptable salts thereof.

This application is a Continuation of U.S. application Ser. No. 13/079,273, filed on Apr. 4, 2011, now allowed, which is a Continuation of National Stage of International Application No. PCT/JP2009/067342, filed on Oct. 5, 2009 and claims benefit to Japanese application No. 2008-258003, field on Oct. 3, 2008.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to glutamic acid derivatives having CaSR agonistic activity or pharmaceutically acceptable salts thereof; and CaSR agonistic agents, pharmaceutical compositions, preventive or therapeutic agents for diarrhea and kokumi-imparting agents each of which comprise the glutamic acid derivative or pharmaceutically acceptable salts thereof as an active ingredient.

BACKGROUND OF THE INVENTION

A calcium sensing receptor (CaSR) is also called a calcium receptor, and such receptor signals regulate various functions in vivo. Thus, there is a possibility that substances having CaSR agonistic activity are useful for treating or preventing various diseases and also useful as kokumi-imparting agents. Patent Literature 1 discloses a method for screening for a kokumi-imparting substance and a kokumi-imparting agent containing a kokumi-imparting substance obtained by the screening method. In the literature, it is found that various low molecular peptides have CaSR agonistic activity. Based on this finding, it discloses that it becomes possible to provide a kokumi-imparting agent which can impart “kokumi”, the taste that cannot be expressed with five basic tastes of sweetness, saltiness, sourness, bitterness and umami, and the taste that enhances marginal tastes of the basic tastes, such as thickness, growth (mouthfullness), continuity, and harmony.

Meanwhile, it is known that a γ-glutamyl anilide derivative can be used for measuring the enzyme activity since it becomes a substrate of γ-glutamyl transferase (refer to Non-patent Literature 1 and Patent Literature 2). However, there is no reference that discloses the relationship of a γ-glutamyl anilide derivative with “a calcium sensing receptor (CaSR) or a G-protein-coupled receptor”, “kokumi” and “diarrhea or hyperparathyroidism”, each of which is disclosed in the present invention. The main use of some publicly known compounds among 3-sulfonic acid, 3-carboxylic acid and 3-nitro derivatives, each of which are particularly preferable in the present invention, are a substrate in measuring the enzyme activity of γ-glutamyl transferase. As other uses, it is slightly known that it is used as an antimicrobial agent or an antiallergic agent (refer to Non-patent Literature 2 and Patent Literature 3) and as a reagent for mass spectrometry (refer to Non-patent Literature 3). Further, it is known that examples of a compound activating CaSR include cinacalcet and similar synthetic low molecular compounds, and γ-glutamyl peptide derivatives such as glutathione (refer to Patent Literature 4 and Non-patent Literature 4). However, they are structurally different from glutamic acid derivatives of the present invention.

Therefore, it is expected to provide more excellent kokumi-imparting agents by searching more varieties of compounds having CaSR agonistic activity. It is also expected to provide CaSR agonistic agents, pharmaceutical compositions and preventive or therapeutic agents for diarrhea.

-   -   Patent Literature 1: WO 2007/055393 A1     -   Patent Literature 2: U.S. Pat. No. 4,087,331     -   Patent Literature 3: JP-A 06-172287     -   Patent Literature 4: WO 2007/055388 A2     -   Non-patent Literature 1: Clinical Chemistry, 22, 2051 (1976)     -   Non-patent Literature 2: Journal of Medicinal Chemistry (1965),         8(3), 398-400     -   Non-patent Literature 3: Analytica Chimica Acta (2004), 519(2),         181-187     -   Non-patent Literature 4: Journal of Biological Chemistry (2006),         281(13), 8864-70

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The object of the present invention is, by searching various kinds of compounds having CaSR agonistic activity, to provide CaSR agonistic agents, pharmaceutical compositions, preventive or therapeutic agents for diarrhea and kokumi-imparting agents each of which comprise the compound.

Means for Solving the Problems

The inventors searched compounds having CaSR agonistic activity, and surprisingly, they found that various γ-glutamic acid derivatives and analogues thereof (hereinafter referred to as glutamic acid derivatives) have an excellent CaSR agonistic activity. Further, they found that the glutamic acid derivatives having CaSR agonistic activity or pharmaceutically acceptable salts thereof can be useful as CaSR agonistic agents, pharmaceutical compositions, preventive or therapeutic agents for diarrhea or kokumi-imparting agents. The present invention has been completed based on these findings.

Namely, the present invention provides a glutamic acid derivative of the following formula (I) or pharmaceutically acceptable salts thereof:

wherein R₁ and R₃-R₅ are each independently selected from the group consisting of a hydrogen atom, a halogeno group, a hydroxyl group, a nitro group, an amino group, an alkyl group having 1 to 6 carbon atoms which may have a substituent(s), an alkoxy group having 1 to 6 carbon atoms which may have a substituent(s) and a mono- or di-alkylamino group having 1 to 6 carbon atoms which may have a substituent(s); R₂ is selected from the group consisting of a nitro group, a sulfonic acid group,

R₆ and R₇ each independently represent a hydrogen atom or an alkyl group having 1 to 6 carbon atoms which may have a substituent(s); and X represents a methylene group or an oxygen atom, provided that the following compounds (i)-(iv) are excluded: (i) a compound wherein X is a methylene group, R₂ is a sulfonic acid group, and each of R₁ and R₃-R₆ is a hydrogen atom; (ii) a compound wherein X is a methylene group, R₂ is a sulfonic acid group, each of R₁ and R₄-R₆ is a hydrogen atom, and R₃ is a nitro group; (iii) a compound wherein X is a methylene group, R₂ is a nitro group, and each of R₁ and R₃-R₆ is a hydrogen atom; and (iv) a compound wherein X is a methylene group, R₂ is

each of R₁ and R₄-R₆ is a hydrogen atom, R₃ is a hydrogen atom, a nitro group, a hydroxyl group, an amino group, a diethylamino group or a di-n-propylamino group, and R₇ is a hydrogen atom or a methyl group.

The present invention also provides a glutamic acid derivative of the following formula (I) or pharmaceutically acceptable salts thereof;

wherein R₂, R₄ and R₅ are each independently selected from the group consisting of a hydrogen atom, a halogeno group, a hydroxyl group, a nitro group, an amino group, an alkyl group having 1 to 6 carbon atoms which may have a substituent(s), an alkoxy group having 1 to 6 carbon atoms which may have a substituent(s) and a mono- or di-alkylamino group having 1 to 6 carbon atoms which may have a substituent(s); either R₁ or R₃ is a sulfonic acid group and the other is selected from the group consisting of a hydrogen atom, a halogeno group, a hydroxyl group, a nitro group, an amino group, an alkyl group having 1 to 6 carbon atoms which may have a substituent(s), an alkoxy group having 1 to 6 carbon atoms which may have a substituent(s) and a mono- or di-alkylamino group having 1 to 6 carbon atoms which may have a substituent(s); R₆ and R₇ each independently represent a hydrogen atom or an alkyl group having 1 to 6 carbon atoms which may have a substituent(s); and X represents a methylene group or an oxygen atom, provided that the following compound is excluded: a compound wherein X is a methylene group, R₁ is a sulfonic acid group, and each of R₂-R₆ is a hydrogen atom.

The present invention also provides a glutamic acid derivative of the following formula (I) or pharmaceutically acceptable salts thereof:

wherein R₁ and R₃-R₅ are each independently selected from the group consisting of a hydrogen atom, a halogeno group, a hydroxyl group, a nitro group, an amino group, an alkyl group having 1 to 6 carbon atoms which may have a substituent(s), an alkoxy group having 1 to 6 carbon atoms which may have a substituent(s) and a mono- or di-alkylamino group having 1 to 6 carbon atoms which may have a substituent(s); R₂ is selected from the group consisting of a nitro group, a sulfonic acid group,

R₆ represents a hydroxyl group; R₇ represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms which may have a substituent(s); and X represents a methylene group or an oxygen atom.

The present invention also provides a pharmaceutical composition comprising a glutamic acid derivative of the following formula (I) or pharmaceutically acceptable salts thereof:

wherein R₁ and R₃-R₅ are each independently selected from the group consisting of a hydrogen atom, a halogeno group, a hydroxyl group, a nitro group, an amino group, an alkyl group having 1 to 6 carbon atoms which may have a substituent(s), an alkoxy group having 1 to 6 carbon atoms which may have a substituent(s) and a mono- or di-alkylamino group having 1 to 6 carbon atoms which may have a substituent(s); R₂ is selected from the group consisting of a nitro group, a sulfonic acid group,

R₆ and R₇ each independently represent a hydrogen atom or an alkyl group having 1 to 6 carbon atoms which may have a substituent(s); and X represents a methylene group or an oxygen atom, provided that the following compound is excluded: a compound wherein X is a methylene group, R₂ is

each of R₁ and R₃-R₆ is a hydrogen atom, and R₇ is a hydrogen atom or a methyl group.

Further, the present invention provides a CaSR agonistic agent, a kokumi-imparting agent or a therapeutic or preventive agent for diarrhea each comprising a glutamic acid derivative of the following formula (I) or pharmaceutically acceptable salts thereof:

wherein R₁-R₅ are each independently selected from the group consisting of a hydrogen atom, a halogeno group, a hydroxyl group, a nitro group, an amino group, an alkyl group having 1 to 6 carbon atoms which may have a substituent(s), an alkoxy group having 1 to 6 carbon atoms which may have a substituent(s), a mono- or di-alkylamino group having 1 to 6 carbon atoms which may have a substituent(s), a sulfonic acid group,

provided that any one of R₁-R₃ is selected from the group consisting of a nitro group, a sulfonic acid group,

R₆ and R₇ each independently represent a hydrogen atom, a hydroxyl group or an alkyl group having 1 to 6 carbon atoms which may have a substituent(s); and X represents a methylene group or an oxygen atom.

The present invention also provides a CaSR agonistic agent, a kokumi-imparting agent or a therapeutic or preventive agent for diarrhea each comprising a glutamic acid derivative of the following formula (I) or pharmaceutically acceptable salts thereof:

wherein R₁ and R₃-R₅ are each independently selected from the group consisting of a hydrogen atom, a halogeno group, a hydroxyl group, a nitro group, an amino group, an alkyl group having 1 to 6 carbon atoms which may have a substituent(s), an alkoxy group having 1 to 6 carbon atoms which may have a substituent(s) and a mono- or di-alkylamino group having 1 to 6 carbon atoms which may have a substituent(s); R₂ is selected from the group consisting of a nitro group, a sulfonic acid group,

R₆ and R₇ each independently represent a hydrogen atom or an alkyl group having 1 to 6 carbon atoms which may have a substituent(s); and X represents a methylene group or an oxygen atom.

Effects of the Present Invention

According to the present invention, it becomes possible to provide various compounds having an excellent CaSR agonistic activity, and CaSR agonistic agents, pharmaceutical compositions, preventive or therapeutic agents for diarrhea and kokumi-imparting agents each of which comprise the compound(s).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagram of the prophylactic activity of Compound No. 1 on diarrhea.

FIG. 2 shows a diagram of the prophylactic activity of Compound No. 7 on diarrhea.

BEST MODE FOR CARRYING OUT THE INVENTION

In the glutamic acid derivative of the above formula (I) of the present invention, it is preferable that R₁ and R₃-R₅ are each independently selected from the group consisting of a hydrogen atom, a halogeno group, a hydroxyl group, a nitro group, an amino group, an alkyl group having 1 to 3 carbon atoms which may have a substituent(s), an alkoxy group having 1 to 3 carbon atoms which may have a substituent(s) and a mono- or di-alkylamino group having 1 to 3 carbon atoms which may have a substituent(s). It is more preferable that R₁ and R₃-R₅ are each independently selected from the group consisting of a hydrogen atom, a chloro or bromo group, a hydroxyl group, a nitro group, an amino group, a methyl group and a methoxy group.

In the above formula (I) of the present invention, R₂ is preferably a sulfonic acid group, a carboxylic acid group or a phosphonic acid group.

Alternatively, either one of R₁ or R₃ may be a sulfonic acid group, and R₄ is preferably a halogeno group at that time.

In the above formula (I) of the present invention, X is preferably a methylene group.

In the glutamic acid derivative of the above formula (I) or pharmaceutically acceptable salts thereof, any one of R₁-R₃ is preferably a sulfonic acid group, a carboxylic acid group or a phosphonic acid group. Among them, R₂ is preferably a sulfonic acid group, a carboxylic acid group or a phosphonic acid group, and particularly preferably a sulfonic acid group.

Particularly, in the above formula (I), when R₂ is a sulfonic acid group, it is preferable that R₁ is a hydrogen atom or a hydroxyl group; R₃ is a hydrogen atom, a chloro group, a hydroxyl group, a methyl group or a methoxy group; R₄ is a hydrogen atom, a chloro group or a nitro group; R₅ is a hydrogen atom, a hydroxyl group, a methyl group or a methoxy group; R₆ is a hydrogen atom or a methyl group; and X is a methylene group or an oxygen atom. In the above formula (I), when R₂ is a sulfonic acid group, it is most preferable that R₁ is a hydrogen atom or a hydroxyl group; R₃ is a hydrogen atom, a chloro group or a methyl group; R₄ is a hydrogen atom or a chloro group; R₅ is a hydrogen atom, a hydroxyl group or a methyl group; R₆ is a hydrogen atom; and X is a methylene group.

In the glutamic acid derivative of the above formula (I) or pharmaceutically acceptable salts thereof, particularly when R₂ is a carboxylic acid group, it is most preferable that R₁ is a hydrogen atom or a hydroxyl group; R₃ is a hydrogen atom; R₄ is a hydrogen atom or a bromo group; R₅ is a hydrogen atom; R₆ is a hydrogen atom; and X is a methylene group.

In the glutamic acid derivative of the above formula (I) or pharmaceutically acceptable salts thereof, particularly when R₂ is —PO(OCH₃)OH or —PO(OH)₂, it is most preferable that R₁ is a hydrogen atom; R₃ is a hydrogen atom; R₄ is a hydrogen atom; R₅ is a hydrogen atom; R₆ is a hydrogen atom; and X is a methylene group.

In the glutamic acid derivative of the above formula (I) or pharmaceutically acceptable salts thereof, particularly when R₂ is a nitro group, it is most preferable that R₁ is a hydrogen atom; R₃ is a hydrogen atom; R₄ is a hydrogen atom; R₅ is a hydrogen atom; R₆ is a hydrogen atom; and X is a methylene group.

The glutamic acid derivative of the above formula (I) is preferably compounds mentioned in Examples. Among them, Compounds 1, 7, 10, 21, 22, 24, 32, 33, 34, 35 and 37 are preferable among them. Particularly, Compounds 7, 10, 21, 22, 24, 32, 33, 34, 35 and 37 are preferable.

Each of an alkyl group, an alkoxy group and a mono- or di-alkylamino group in the above formula (I) may have a substituent(s). Examples of a substituent include halogens, a hydroxyl group, an alkoxy group, an amino group, a mono- or di-alkylamino group, a carboxyl group and a sulfonic acid group, but it is not limited to those. Further, an alkoxy group and a mono- or di-alkylamino group as the substituent is preferably a lower alkoxy group and a lower mono- or di-alkylamino group, respectively. “Lower” means that a number of carbons in all substituents are 1 to 3.

In the present invention, marketed products can be used as the glutamic acid derivative of the above formula (I) or pharmaceutically acceptable salts thereof. The glutamic acid derivative or pharmaceutically acceptable salts thereof can also be obtained by preferable publicly-known method such as (1) chemical synthesis and (2) synthesis by enzyme reaction. In the present invention, it is easy to use the method of chemically synthesizing the glutamic acid derivative of the above formula (I) or pharmaceutically acceptable salts thereof as mentioned in Examples. Examples of the chemical synthesis include liquid-phase synthesis and solid-phase synthesis.

The synthesized glutamic acid derivative can be purified with the ordinary method such as ion-exchange chromatography, reversed-phase high-performance liquid chromatography, affinity chromatography and recrystallization. The above chemical synthesis and subsequent purification are well known in this technical field.

The glutamic acid derivative of the above formula (I) of the present invention may be in the form of pharmaceutically acceptable salts thereof. Examples of the pharmaceutically acceptable salts of the glutamic acid derivative of the above formula (I) of the present invention include edible salts. For example, to acidic groups such as a carboxyl group and a sulfonic acid group in the formula (I), the salts include ammonium salts; salts with alkali metals such as sodium and potassium; salts with alkaline earth metals such as calcium and magnesium; aluminum salts; zinc salts; salts with organic amines such as triethylamine, ethanolamine, morpholine, pyrrolidine, piperidine, piperazine and dicyclohexylamine; and salts with basic amino acids such as arginine and lysine. When a basic group(s) exists in the formula (I), to such basic groups, the salts include salts with inorganic acids such as a hydrochloric acid, a sulfuric acid, a phosphoric acid, a nitric acid and a hydrobromic acid; salts with organic carboxylic acids such as an acetic acid, a citric acid, a benzoic acid, a maleic acid, a fumaric acid, a tartaric acid, a succinic acid, a tannic acid, a butyric acid, a hibenzic acid, a pamoic acid, an enanthic acid, a decanoic acid, a teoclate, a salicylic acid, a lactic acid, an oxalic acid, a mandelic acid and a malic acid; and salts with organic sulfonic acids such as a methane sulfonic acid, a benzene sulfonic acid and a p-toluene sulfonic acid.

In the specification, “CaSR” indicates a calcium sensing receptor, and it belongs to the class C of seven transmembrane receptors. It is also called a calcium receptor. A “CaSR agonist” indicates a compound bonding to CaSR and activating CaSR. A “CaSR agonistic agent” indicates an agent or a substance bonding to CaSR and activating CaSR. Further, “activating CaSR” indicates that a ligand bonds to CaSR and thereby activates guanine nucleotide-binding proteins to transmit signals. The behavior that a compound bonds to CaSR and activates CaSR is called “CaSR agonistic activity”.

The method for screening for a compound having CaSR agonistic activity are specifically illustrated as follows, but it is not limited to these steps.

1) Add a tested substance to CaSR activity measurement system for measuring CaSR activity and measure the CaSR activity thereof.

2) Compare the CaSR activity when adding a tested substance and the CaSR activity without adding it.

3) Select a tested substance that CaSR agonistic activity is shown when adding the tested substance.

The measurement of CaSR activity can be conducted by the measurement system with cells expressing CaSR, for example. The cells may be those internally expressing CaSR or recombinant cells externally introducing CaSR genes. Any CaSR activity measurement system is usable without limitation, provided that, when adding a CaSR-specific extracellular ligand (an activating substance) to the cells expressing CaSR, the system can detect the binding (reaction) of the activating substance to CaSR or it can transmit detectable signals in the cells in response to the binding (reaction) of the activating substance to CaSR. When CaSR activity is detected by the reaction with a tested substance, it is determined that the tested substance has CaSR stimulating activity.

A preferable example of CaSR includes human CaSR encoded by the human CaSR gene which is registered as GenBank Accession No. NM_(—)000388. Meanwhile, CaSR is not limited to the protein encoded by the gene of the above sequence. Insofar as proteins having CaSR function are encoded, the proteins may be those encoded by the gene sharing 60% or more, preferably 80% or more, and more preferably 90% or more of homology with the above sequence. The CaSR function can be examined by expressing the above genes in cells and measuring changes of current and changes of intracellular calcium ion concentration in calcium addition.

The origin of CaSR is not particularly limited, and in addition to the human CaSR, examples thereof include any animal-derived CaSR such as those of mouse, rat and canine.

As mentioned above, CaSR activity can be confirmed by using living cells expressing CaSR or fragments thereof cell membranes expressing CaSR or fragments thereof the in vitro system containing proteins of CaSR fragments thereof.

The measurement of CaSR activity with living cells is illustrated below as one example, but it is not limited to the following.

CaSR is expressed in culture cells such as Xenopus oocytes, hamster ovary cells and human embryonic kidney cells. The expression becomes possible by cloning a CaSR gene to a plasmid having a foreign gene; and then introducing cRNA of the plasmid or cRNA generated from the plasmid template. The electrophysiological method, a fluorescent indicating reagent for detecting increase of intracellular calcium, or the like can be used for detecting the reaction.

The expression of CaSR is first confirmed by a response by calcium or a specifically activating agent.

An oocyte wherein the intracellular current was observed or a culture cell wherein fluorescence of a fluorescent indicating reagent was observed is used to calcium of around 5 mM concentration. The concentration of calcium is changed, and concentration dependence thereof is measured. Next, a tested substance is prepared to become 1 μM to 1 mM, and added to an oocyte or a culture cell. Then, CaSR activity thereof in the presence of the tested substance is measured to measure CaSR agonistic activity of the tested substance.

The CaSR agonistic agent can comprise any glutamic acid derivative or pharmaceutically acceptable salts thereof included in a glutamic acid derivative of the above formula (I) alone or in combinations with preferable two or more kinds thereof. Further, the agent can comprise any solid or liquid carrier or additives each of which is pharmaceutically, physiologically and experimentally acceptable and also acceptable as a food product.

Examples of the carrier include glucose, lactose, sucrose, starch, mannitol, dextrin, glycerides of fatty acids, polyethylene glycols, hydroxyethyl starch, ethylene glycols, polyoxyethylene sorbitan fatty acid ester, gelatin, albumin, amino acids, water and a normal saline solution. If necessary, common additives such as stabilizing agents, moisturizing agents, emulsifying agents, binders and tonicity agents can be preferably added to the CaSR agonistic agent of the present invention.

The above additives are not particularly limited as long as they are usually used for purposes corresponding to the purposes. Examples of the additives include flavoring agents, sugars, sweetening agents, dietary fibers, vitamins, amino acids such as a monosodium glutamate (MSG), nucleic acids such as an inosine monophosphate (IMP), inorganic salts such as sodium chloride and water.

The CaSR agonistic agent of the present invention can be used in any form without limitation of properties, such as dry powder, paste and a solution. Further, the CaSR agonistic agent of the present invention can be used in medical drugs, quasi drugs, food products, reagents, or the like.

The usage amount of the CaSR agonistic agent of the present invention can be preferably adjusted corresponding to purposes. For example, in the case of orally administering the agent to a target, a total amount of a glutamic acid derivative of the formula (I) or pharmaceutically acceptable salts thereof is preferably 0.01 to 10 g per 1 kg of body weight in one administration, and more preferably 0.1 to 1 g.

The frequency of administration is not particularly limited, and the agent can be administered once or several times per day.

In the case of using the CaSR agonistic agent of the present invention in food products or reagents, 0.000001 to 10 g per one prescription is preferable, and 0.00001 to 1 g per one prescription is more preferable.

The content of the glutamic acid derivative of the formula (I) or pharmaceutically acceptable salts thereof in the CaSR agonistic agent of the present invention is not particularly limited only if it fits the usage amount mentioned above. The content thereof is preferably 0.000001 to 99.9999 weight % per dry weight, more preferably 0.00001 to 99.999 weight %, and particularly preferably 0.0001 to 99.99 weight %.

The CaSR agonistic agent of the present invention can further contain one or more kinds of a known substance(s) having CaSR agonistic activity.

Examples of the known substance having CaSR agonistic activity include cations such as calcium and gadolinium; basic peptides such as polyarginine and polylysine; polyamines such as putrescine, spermine and spermidine; proteins such as protamine; amino acids such as phenylalanine; peptides such as glutathione; and analogues of cinacalcet, but it is not limited to those.

Further, in addition to the known substance having CaSR agonistic activity, the CaSR agonistic agent of the present invention can contain any known substance corresponding to purposes.

“Kokumi” in the specification indicates the taste that cannot be expressed with five basic tastes of sweetness, saltiness, sourness, bitterness and umami, and the taste that enhances marginal tastes of the basic tastes, such as thickness, growth (mouthfullness), continuity, and harmony. A “kokumi-imparting agent” indicates an agent or a substance that can enhance at least one of the five basic tastes of sweetness, saltiness, sourness, bitterness and umami, and impart the marginal tastes of the basic tastes such as thickness, growth (mouthfullness), continuity, and harmony. Accordingly, the kokumi-imparting agent of the present invention can be used as a sweet taste enhancing agent, a salty taste enhancing agent, a sour taste enhancing agent, a bitter taste enhancing agent or an umami taste enhancing agent together with improving the quality of taste.

The kokumi-imparting effects can be confirmed by the method such as a gustatory test by a human being as mentioned in Examples of the present invention, but it is not limited to those.

The kokumi-imparting agent of the present invention can comprise any glutamic acid derivative or pharmaceutically acceptable salts thereof included in a glutamic acid derivative of the above formula (I) alone or in combinations with preferable two or more kinds thereof. Further, various other additives can be preferably added to the kokumi-imparting agent.

The above additives can be used without limitation as long as it is known that they can be added or dispensed to foods and beverages such as seasonings, food products and beverages. Examples of the additives include flavoring agents, sugars, sweetening agents, dietary fibers, vitamins, amino acids such as a monosodium glutamate (MSG), nucleic acids such as an inosine monophosphate (IMP), inorganic salts such as sodium chloride and water.

The present invention also provides foods and beverages comprising a glutamic acid derivative of the above formula (I). The usage amount of the glutamic acid derivative of the above formula (I) of the present invention or pharmaceutically acceptable salts thereof or a kokumi-imparting agent to foods and beverages can be the amount effective at imparting kokumi and preferably adjusted depending on the use thereof. For example, in the case of using it in seasonings, food products or beverages, a total amount of a glutamic acid derivative of the above formula (I) of the present invention or pharmaceutically acceptable salts thereof or a kokumi-imparting agent is 1 ppb weight to 99.9 weight % in a seasoning, food or beverage, and more preferably 10 ppb weight to 99.9 weight %.

Accordingly, it is possible to produce kokumi-imparted foods and beverages by adding one or more kinds of a glutamic acid derivative of the above formula (I) of the present invention or pharmaceutically acceptable salts thereof or a kokumi-imparting agent to a food or a beverage so that 1 ppb weight to 99.9 weight %, and preferably 10 ppb weight to 99.9 weight % thereof can be contained in the food or the beverage.

Further, it is also possible to produce kokumi-imparted foods and beverages by adding a kokumi-imparted seasoning(s) which comprises 1 ppb weight to 99.9 weight % of one or more kinds of a glutamic acid derivative of the above formula (I) of the present invention or pharmaceutically acceptable salts thereof to a food or a beverage so that 0.01 to 10 weight %, and preferably 0.1 to 10 weight % of the seasoning(s) can be contained in the food or the beverage.

The kokumi-imparting agent of the present invention can further contain one or more kinds of a known substance(s) having CaSR agonistic activity.

Examples of the known substance having CaSR agonistic activity include cations such as calcium and gadolinium; basic peptides such as polyarginine and polylysine; polyamines such as putrescine, spermine and spermidine; proteins such as protamine; amino acids such as phenylalanine; peptides such as glutathione; and analogues of cinacalcet, but it is not limited to those.

Further, in addition to the known substance having CaSR agonistic activity, the kokumi-imparting agent of the present invention can contain any known substance corresponding to purposes.

When adding a glutamic acid derivative of the above formula (I) of the present invention or pharmaceutically acceptable salts thereof or a kokumi-imparting agent to foods and beverages, any form thereof can be used without limitation of properties, such as dry powder, paste and a solution.

The pharmaceutical composition of the present invention can comprise any glutamic acid derivative or pharmaceutically acceptable salts thereof included in a glutamic acid derivative of the above formula (I) alone or in combinations with preferable two or more kinds thereof.

The usage amount of the pharmaceutical composition of the present invention can be preferably adjusted corresponding to purposes. For example, in the case of orally administering the pharmaceutical composition to a target, a total amount of a glutamic acid derivative of the formula (I) or pharmaceutically acceptable salts thereof is preferably 0.01 to 10 g per 1 kg of body weight in one administration, and more preferably 0.1 to 1 g. The frequency of administration is not particularly limited, and the composition can be administered once or several times per day.

In the case of using the pharmaceutical composition of the present invention in food products or reagents, 0.001 to 10 g per one prescription is preferable, and 0.01 to 1 g per one prescription is more preferable.

The content of the glutamic acid derivative of the formula (I) or pharmaceutically acceptable salts thereof in the pharmaceutical composition of the present invention is not particularly limited only if it fits the usage amount mentioned above. The content thereof is preferably 0.000001 to 99.9999 weight % per dry weight, more preferably 0.00001 to 99.999 weight %, and particularly preferably 0.0001 to 99.99 weight %.

The pharmaceutical composition of the present invention can further contain one or more kinds of a known substance(s) having CaSR agonistic activity.

Examples of the known substance having CaSR agonistic activity include cations such as calcium and gadolinium; basic peptides such as polyarginine and polylysine; polyamines such as putrescine, spermine and spermidine; proteins such as protamine; amino acids such as phenylalanine; peptides such as glutathione; and analogues of cinacalcet, but it is not limited to those.

Further, in addition to the known substance having CaSR agonistic activity, the pharmaceutical composition of the present invention can contain any known substance corresponding to purposes.

The method of applying the pharmaceutical composition of the present invention is not particularly limited, and any invasive or non-invasive administration such as oral administration and injection is applicable. Suppository or transdermal administration is also applicable. It is possible to administer an active ingredient by formulating it into a common pharmaceutical preparation form together with a solid or liquid pharmaceutical carrier that is suitable for the administration method such as oral administration and injection. Examples of the preparation form include solid agents such as tablets, granules, powders and capsules; liquid agents such as solutions, suspensions and emulsifying agents; and freeze-drying agents. These preparations can be prepared by common maneuver in pharmaceutical preparations. Further, any solid or liquid carrier or additives each of which is pharmaceutically and physiologically acceptable can be added to the pharmaceutical composition of the present invention.

Examples of the carrier include glucose, lactose, sucrose, starch, mannitol, dextrin, glycerides of fatty acids, polyethylene glycols, hydroxyethyl starch, ethylene glycols, polyoxyethylene sorbitan fatty acid ester, gelatin, albumin, amino acids, water and a normal saline solution. If necessary, common additives such as stabilizing agents, moisturizing agents, emulsifying agents, binders and tonicity agents can be preferably added to the pharmaceutical composition of the present invention.

In the specification, diarrhea includes all kinds of diarrhea such as irritable colon syndrome, functional diarrhea, inflammatory bowel disease, diverticulitis, bacterial diarrhea and dyspepsia.

The therapeutic or preventive agent for diarrhea of the present invention can comprise any glutamic acid derivative or pharmaceutically acceptable salts thereof included in a glutamic acid derivative of the above formula (I) alone or in combinations with preferable two or more kinds thereof.

The usage amount of the therapeutic or preventive agent for diarrhea of the present invention can be preferably adjusted corresponding to purposes. For example, in the case of orally administering the agent to a target, a total amount of a glutamic acid derivative of the formula (I) or pharmaceutically acceptable salts thereof is preferably 0.01 to 10 g per 1 kg of body weight in one administration, and more preferably 0.1 to 1 g. The frequency of administration is not particularly limited, and the agent can be administered once or several times per day.

In the case of using the therapeutic or preventive agent for diarrhea of the present invention in food products or reagents, 0.001 to 10 g per one prescription is preferable, and 0.01 to 1 g per one prescription is more preferable.

The content of the glutamic acid derivative of the formula (I) or pharmaceutically acceptable salts thereof in the therapeutic or preventive agent for diarrhea of the present invention is not particularly limited only if it fits the usage amount mentioned above. The content thereof is preferably 0.000001 to 99.9999 weight % per dry weight, more preferably 0.00001 to 99.999 weight %, and particularly preferably 0.0001 to 99.99 weight %.

The therapeutic or preventive agent for diarrhea of the present invention can further contain one or more kinds of a known substance(s) having CaSR agonistic activity.

Examples of the known substance having CaSR agonistic activity include cations such as calcium and gadolinium; basic peptides such as polyarginine and polylysine; polyamines such as putrescine, spermine and spermidine; proteins such as protamine; amino acids such as phenylalanine; peptides such as glutathione; and analogues of cinacalcet, but it is not limited to those.

Further, in addition to the known substance having CaSR agonistic activity, the therapeutic or preventive agent for diarrhea of the present invention can contain any known substance corresponding to purposes.

The method of applying the therapeutic or preventive agent for diarrhea of the present invention is not particularly limited, and any invasive or non-invasive administration such as oral administration and injection is applicable. Suppository or transdermal administration is also applicable. It is possible to administer an active ingredient by formulating it into a common pharmaceutical preparation form together with a solid or liquid pharmaceutical carrier that is suitable for the administration method such as oral administration and injection. Examples of the preparation form include solid agents such as tablets, granules, powders and capsules; liquid agents such as solutions, suspensions and emulsifying agents; and freeze-drying agents. These preparations can be prepared by common maneuver in pharmaceutical preparations. Further, any solid or liquid carrier or additives each of which is pharmaceutically and physiologically acceptable can be added to the therapeutic or preventive agent for diarrhea of the present invention.

Examples of the carrier include glucose, lactose, sucrose, starch, mannitol, dextrin, glycerides of fatty acids, polyethylene glycols, hydroxyethyl starch, ethylene glycols, polyoxyethylene sorbitan fatty acid ester, gelatin, albumin, amino acids, water and a normal saline solution. If necessary, common additives such as stabilizing agents, moisturizing agents, emulsifying agents, binders and tonicity agents can be preferably added to the therapeutic or preventive agent for diarrhea of the present invention.

The CaSR agonistic agent, kokumi-imparting agent, and therapeutic or preventive agent for diarrhea of the present invention can be used as foods and beverages or supplements wherein each agent has each effect. For example, it is possible to prepare foods and beverages indicating on the container or package thereof that it has a therapeutic or preventive effect on diarrhea. The form of the foods and beverages is not particularly limited, and the foods and beverages can be produced by the same production method as that of usual food products, using the same materials used in producing such food products, except that a compound(s) having CaSR agonistic activity is dispensed. Examples of food products include seasonings; beverages such as juice and milk; confectionery; jellies; health foods; processed agricultural products; processed animal products such as milk and cheese; and food supplements.

(Representative Method of Synthesizing a Glutamic Acid Derivative of the Formula (I))

The representative method of producing the compound of the present invention is illustrated below.

In the following production method, it is production-technologically effective in some kinds of functional groups that the functional group is substituted with a preferable protective group, i.e. a group that can be easily converted into the functional group during the functional group is in a raw material or intermediate. After that, the protective group is removed if necessary to obtain the intended compound. Examples of the functional group include an amino group, a hydroxyl group and a carboxyl group. Further, examples of the protective group thereof include t-butoxycarbonyl (Boc), benzyloxycarbonyl (Z or Cbz) and 9-fluorenylmethoxycarbonyl (Fmoc) as a protective group of an amino group; t-butyl (tBu) and benzyl (Bn or Bzl) as a protective group of a carboxyl group; and protective groups described on the third edition of Protective Groups in Organic Synthesis (T. W. Green and P. G. M. Wuts, JOHN WILLY & SONS, INC.) They can be preferably used corresponding to the reaction conditions. The introduction and deprotection of a protective group can be conducted at the right time in accordance with the method described on the above referential literature. For example, functional groups represented as Prot1 and Prot2 in the following production methods 1 and 2 indicate that they are used as protective groups, but functional groups are not limited to those.

The production method 1 is a reaction comprising the step of conducting a condensation reaction of a carboxylic acid and an amine with a compound (II) and a compound (III) to obtain a compound (I).

This reaction can be conducted in accordance with the ordinary method wherein a compound (II) and an amine derivative (III) are used equivalently or one of them is used excessively in the presence of a condensation agent. Preferable examples of a condensation agent include N,N-dicyclohexylcarbodiimide (DCC), 1-ethyl-3-[3-(N,N-dimethylamino) propyl]carbodiimide (EDCI or WSC), O-benzotriazole-1-yl-N,N,N′,N′-tetramethyluronium hexafluorophosphate (HBTU), carbonyldiimidazole (CDI), 4-(4,6-dimethoxy-1,3,5-triazin-2-yl) 4-methylmorphonium chloride (DMTMM), and 2-(7-azabenzotriazole-1-yl)-N,N,N′,N′-tetramethyluronium hexafluorophosphate (HATU). These condensation agents are used equivalently or excessively to a carboxylic acid. As for a solvent, those that are not involved in the reaction can be used. Examples of a solvent include N,N-dimethylformamide (DMF), dioxane, water, methanol, ethanol, tetrahydrofuran (THF), dichloromethane, dichloroethane, diethylether, chloroform, dimethoxyethane (DME), ethyl acetate, toluene, acetonitrile, dimethylsulfoxide (DMSO), and a mixed solvent thereof. It is preferable to preferably select a solvent depending on a raw material, the kind of a condensation agent, and the like. The reaction can smoothly proceed in the presence of a base such as triethylamine, diisopropylethylamine, N-methylmorpholine, pyridine and 4-dimethylaminopyridine; or by reacting said base(s) as a solvent. Though the reaction is usually conducted at cooling or room temperature, it is sometime preferable that the reaction is conducted under heating depending on the conditions of the condensation reaction.

Further, the compound (I) can be produced by the method comprising the steps of introducing a carboxylic acid into an active derivative, and condensing it with an amine. In this case, the compound (II) and the amine derivative (III) are used equivalently or one of them is used excessively. Examples of an active derivative of a carboxylic acid include phenol compounds such as p-nitrophenol; active esters obtained by reacting N-hydroxyamine compounds such as 1-hydroxysuccinimide (HOSu), 1-hydroxybenzotriazole (HOBt) and 7-aza-1-hydroxybenzotriazole (HOAt); mixed acid anhydrides obtained by reacting monoalkyl carbonate and an organic acid; phosphoric mixed acid anhydrides obtained by reacting diphenylphosphoryl chloride and N-methylmorpholine; acid azides obtained by reacting an ester with hydrazine and an alkyl nitrite successively; acid halides such as acid chlorides and acid fluorides; and symmetrical acid anhydrides.

When synthesizing an active derivative of a carboxylic acid, an activating reagent is used equivalently or excessively to the compound (II). Other than said reaction conditions, any reaction can be used provided that it is a reaction that an amide binding is formed.

The production method 2 is a reaction comprising the steps of obtaining an intermediate from a compound (IIa) and acting a compound (III) on the obtained intermediate to obtain a compound (I).

In the reaction, an intermediate can be obtained by acting a compound (IIa) with an equivalent or a little excessive reagent such as N,N-carbonyldiimidazole, phosgene, triphosgene, benzyl chloroformate and methyl carbonate. At that time, it is preferable to conduct the reaction using a solvent that is not involved in the reaction, e.g., N, N-dimethylformamide (DMF), dioxane, tetrahydrofuran (THF), dichloromethane, dichloroethane, diethylether, chloroform, dimethoxyethane (DME), ethyl acetate, toluene, acetonitrile, dimethylsulfoxide (DMSO), and a mixed solvent thereof. Though the reaction is usually conducted at cooling or room temperature, it is sometime preferable that the reaction is conducted under heating depending on the kinds of a reagent and a compound. The obtained intermediate is, if necessary, substituted to a preferable solvent, and the reaction is conducted using the intermediate and the compound (III) equivalently or using one of them a little excessively. In the reaction, it is possible to make an organic base such as triethylamine or an inorganic base such as potassium carbonate coexist. Though the reaction is usually conducted under cooling to under heating of around 100° C., it is sometime preferable to conduct the reaction under further heating depending on the kind of a compound. Other than the above method, any reaction can be used provided that it is a reaction that a carbamate is formed.

(Production Method 3)

Thus produced compound of the present invention can be used as a free compound as itself, or can be isolated or purified as salts thereof with common chemical operations such as extraction, precipitation, fractional chromatography, fractional crystallization and recrystallization. The salts of the compound can be produced by conducting a general salt-forming reaction to the free compound of the present invention.

Further, when the compound of the present invention has asymmetric carbons, optical isomers exist. The optical isomers can be produced by the method comprising the steps of introducing the compound into a diastereomeric salt with an optically active acid or base, and fractionally-crystallizing it; the optical resolution method with the ordinary method such as column chromatography; or the synthesis method with an optically active raw compound.

EXAMPLES

Next, Examples will further illustrate the present invention. They only explain the present invention and do not particularly limit the invention.

In the specification, the ordinary method indicates the method generally used as a chemical operation such as liquid separation, drying, filtration and concentration.

In the specification, a purification process A indicates the method comprising the steps of putting a crude substance obtained by the ordinary method in a reverse-phase high-performance liquid chromatography using octadecylsilyl silica gel as a filler, eluting it with a mixed solution of water and acetonitrile that contains a 0.1% (v/v) trifluoroacetic acid, and concentrating and freeze-drying an intended fraction.

The following examples will further illustrate synthesis of the representative compounds of the present invention shown in Table 1. They only explain the compounds of the present invention and do not particularly limit them.

TABLE 1 Comp. No. R₁ R₂ R₃ R₄ R₅ R₆ X 1 H SO₃H H H H H CH₂ 2 H SO₃H OMe H H H CH₂ 3 H SO₃H H H OMe H CH₂ 4 H SO₃H Me H Me H CH₂ 5 H SO₃H Me H H H CH₂ 6 H SO₃H H NO₂ OH H CH₂ 7 OH SO₃H H Cl H H CH₂ 8 H SO₃H H H OH H CH₂ 9 H SO₃H Cl H H H CH₂ 10 OH SO₃H H H H H CH₂ 11 H SO₃H OH H H H CH₂ 12 H SO₃H H H H CH₃ CH₂ 13 H SO₃H H H H H O 14 H CO₂H H H H H CH₂ 15 OH CO₂H H H H H CH₂ 16 H CO₂H H Br H H CH₂ 17 H PO(OMe)OH H H H H CH₂ 18 H PO(OH)₂ H H H H CH₂ 19 H NO₂ H H H H CH₂ 20 H H H H H H CH₂

Example I Synthetic Example 1 Synthesis of N⁵-(3-sulfophenyl)-L-glutamine (Compound No. 1)

Boc-Glu-OtBu (75 mg, 0.247 mmol), HATU (112 mg, 0.296 mmol) and HOAt (41 mg, 0.296 mmol) were dissolved in 1 mL of DMF. Triethylamine (52 μL) was added thereto and stirred at room temperature for 10 minutes. 3-Sulfoaniline (43 mg, 0.247 mmol) was added thereto and stirred overnight at room temperature. After removing a solvent, purification was conducted in accordance with the purification process A. The obtained intermediate was dissolved in 2 mL of a trifluoroacetic acid and stirred at room temperature for 3 hours, and a solvent was removed therefrom. The obtained product was purified in accordance with the purification process A to obtain a title compound.

Yield amount: 30.8 mg (0.10 mmol) yield: 41%

1H-NMR (D2O, 300 MHz): δ 7.89 (s, 1H), 7.67-7.62 (m, 2H), 7.58-7.53 (m, 1H), 3.99 (t, 1H, J=6.4 Hz), 2.73-2.66 (m, 2H), 2.33-2.25 (m, 2H)

ESI (m/z): 303 [M+H]+, 301 [M−H]−

Synthetic Example 2 Synthesis of N⁵-(4-methoxy-3-sulfophenyl)-L-glutamine (Compound No. 2)

A title compound was obtained by the same method as that of the synthetic example 1 except that p-anisidine-3-sulfonic acid was used instead of 3-sulfoaniline.

Yield amount: 24.7 mg yield: 23%

1H-NMR (D2O, 300 MHz): δ 7.96 (s, 1H), 7.53 (d, 1H), 7.04 (d, 1H), 3.98 (t, 1H), 3.78 (s, 3H), 2.63-2.52 (m, 2H), 2.30-2.05 (m, 2H)

ESI (m/z): 333 [M+H]+

Synthetic Example 3 Synthesis of N⁵-(2-methoxy-5-sulfophenyl)-L-glutamine (Compound No. 3)

A title compound was obtained by the same method as that of the synthetic example 1 except that o-anisidine-5-sulfonic acid was used instead of 3-sulfoaniline.

Yield amount: 75.7 mg yield: 69%

1H-NMR (D2O, 300 MHz): δ 7.65 (s, 1H), 7.45 (d, 1H), 7.04 (d, 1H), 3.96 (t, 1H), 3.79 (s, 3H), 2.80-2.50 (m, 2H), 2.25-2.10 (m, 2H)

ESI (m/z): 333 [M+H]+

Synthetic Example 4 Synthesis of N⁵-(2,4-dimethyl-5-sulfophenyl)-L-glutamine (Compound No. 4)

A title compound was obtained by the same method as that of the synthetic example 1 except that 2,4-dimethylaniline-5-sulfonic acid sodium salt was used instead of 3-sulfoaniline.

Yield amount: 70.3 mg yield: 64%

1H-NMR (D2O, 300 MHz): δ 7.55 (s, 1H), 7.17 (s, 1H), 3.97 (t, 1H), 2.67-2.55 (m, 2H), 2.43 (s, 3H), 2.30-2.15 (m, 2H), 2.08 (s, 3H)

ESI (m/z): 331 [M+H]+

Synthetic Example 5 Synthesis of N⁵-(4-methyl-3-sulfophenyl)-L-glutamine (Compound No. 5)

A title compound was obtained by the same method as that of the synthetic example 1 except that 5-amino-2-methylbenzene-1-sulfonic acid was used instead of 3-sulfoaniline.

Yield amount: 79.3 mg yield: 76%

1H-NMR (D2O, 300 MHz): δ 7.76 (s, 1H), 7.34 (d, 1H), 7.24 (d, 1H), 3.93 (t, 1H), 2.60-2.45 (m, 2H), 2.44 (s, 3H), 2.30-2.00 (m, 2H)

ESI (m/z): 317 [M+H]+

(Synthetic Example 6) Synthesis of N⁵-(2-hydroxy-3-nitro-5-sulfophenyl)-L-glutamine (Compound No. 6)

A title compound was obtained by the same method as that of the synthetic example 1 except that 3-amino-4-hydroxy-5-nitrobenzene-sulfonic acid was used instead of 3-sulfoaniline.

Yield amount: 73.8 mg yield: 62%

1H-NMR (D2O, 300 MHz): δ 8.37 (s, 1H), 8.24 (s, 1H), 3.94 (t, 2.64-2.70 (m, 2H), 2.09-2.23 (m, 2H)

ESI (m/z): 364 [M+H]+

Synthetic Example 7 Synthesis of N⁵-(5-chloro-2-hydroxy-3-sulfophenyl)-L-glutamine (Compound No. 7)

Boc-Glu-OtBu (100 mg, 0.33 mmol) and HOBt hydrate (65.6 mg, 0.43 mmol) were dissolved in 2 mL of DMF, and triethylamine (0.137 mL) was added thereto. After cooling the mixture down to 0° C., diisopropylcarbodiimide (66.4 μL, 0.43 mmol) and 2-amino-4-chlorophenol-6-sulfonic acid (73.7 mg, 0.33 mmol) were added thereto and stirred overnight at room temperature. After removing a solvent, purification was conducted in accordance with the purification process A. The obtained intermediate was dissolved in 2 mL of TFA and stirred at room temperature for 2 hours. 2 mL of methylene chloride was added thereto, and a precipitate was taken by filtration to obtain a title compound.

Yield amount: 16.8 mg yield: 14.4%

1H-NMR (DMSO-d6, 300 MHz): δ 11.07 (s, 1H), 9.39 (s, 1H), 8.20-8.40 (br, 2H), 8.02 (s, 1H), 7.14 (s, 1H), 3.95 (t, 1H, J=6.4 Hz), 2.64 (m, 2H), 2.07 (m, 2H)

ESI (m/z): 353 [M+H]+

Synthetic Example 8 Synthesis of N⁵-(2-hydroxy-5-sulfophenyl)-L-glutamine (Compound No. 8)

A title compound was obtained by the same method as that of the synthetic example 7 except that 2-aminophenol-4-sulfonic acid was used instead of 2-amino-4-chlorophenol-6-sulfonic acid.

Yield amount: 31.5 mg yield: 30%

1H-NMR (D2O, 300 MHz): δ 7.77 (s, 1H), 7.44 (d, 1H), 6.94 (d, 1H), 4.00-3.85 (m, 1H), 2.65-2.57 (m, 2H), 2.19-2.10 (m, 2H)

ESI (m/z): 319 [M+H]+

Synthetic Example 9 Synthesis of N⁵-(4-chloro-3-sulfophenyl)-L-glutamine (Compound No. 9)

A title compound was obtained by the same method as that of the synthetic example 7 except that 4-chloroaniline-3-sulfonic acid (68.4 mg) was used instead of 2-amino-4-chlorophenol-6-sulfonic acid.

Yield amount: 47.8 mg yield: 43%

1H-NMR (D2O, 300 MHz): δ 7.91 (s, 1H), 7.50-7.45 (m, 2H), 4.00-3.85 (m, 1H), 2.60-2.40 (m, 1H), 2.25-2.15 (m, 2H)

ESI (m/z): 337 [M+H]+

Synthetic Example 10 Synthesis of N⁵-(2-hydroxy-3-sulfophenyl)-L-glutamine (Compound No. 10)

Z-Glu-OBn (371 mg, 1 mmol) was dissolved in methylene chloride (1 mL), and CDI (180 mg, 1.1 mmol) was added thereto and stirred at room temperature for 30 minutes. Then, 2-amino-4-chlorophenol-6-sulfonic acid (223 mg, 1 mmol) and THF (1 mL) were added thereto and stirred overnight at room temperature. After removing a solvent, purification was conducted in accordance with the purification process A. The obtained intermediate was dissolved in a mixed solvent of methanol and water. Pd/C in catalyst quantity was added thereto and stirred under hydrogen atmosphere overnight at room temperature. After filtering out the catalyst and removing a solvent, purification was conducted in accordance with the purification process A to obtain a title compound.

Yield amount: 120 mg (0.40 mmol) yield: 40%

1H-NMR (D2O, 300 MHz): δ 7.67 (d, 1H, J=7.9 Hz), 7.62 (d, 1H, J=8.2 Hz), 7.07 (dd, 1H, J=7.9 Hz, 8.2 Hz), 3.92-3.97 (m, 1H), 2.59-2.64 (m, 2H), 2.25-2.20 (m, 2H)

ESI (m/z): 303 [M+H]+

Synthetic Example 11 Synthesis of N⁵-(4-hydroxy-3-sulfophenyl)-L-glutamine (Compound No. 11)

Boc-Glu-OtBu (100 mg, 0.33 mmol) was dissolved in methylene chloride (1 mL) and THF (1 mL). CDI (65 mg, 1.1 mmol) was added thereto and stirred at room temperature for 30 minutes. Then, 5-amino-2-hydroxybenzene sulfonic acid salt (77 mg, 0.33 mmol) was added thereto and stirred overnight at room temperature. After removing a solvent, purification was conducted in accordance with the purification process A. The obtained intermediate was dissolved in 2 mL of TFA and stirred at room temperature for 3 hours, and a solvent was removed therefrom. The obtained product was purified in accordance with the purification process A to obtain a title compound.

Yield amount: 2 mg

ESI (m/z): 319 [M+H]+

Synthetic Example 12 Synthesis of N⁵-methyl-N⁵-(3-sulfophenyl)-L-glutamine (Compound No. 12) Step 1 Synthesis of 3-[(2-nitrophenyl)sulfonyl]aminobenzenesulfonic acid

3-Aminobenzenesulfonic acid (346.3 mg, 2 mmol) was suspended in 2.5 mL of methylene chloride. After cooling the mixture down to 0° C., 2-nitrophenyl benzenesulfonylchloride (443.2 mg, 2 mmol) and N,N-diisopropylethylamine (697 μL, 4 mmol) were added thereto and stirred at room temperature for 1 hour. The solvent was removed therefrom, and purification was conducted in accordance with the purification process A to obtain a title compound.

Yield amount: 460 mg (1.29 mmol) yield: 64%

1H-NMR (DMSO-d6, 300 MHz): δ 7.02-7.83 (m, 8H)

ESI (m/z): 359 [M+H]+

Step 2 Synthesis of N⁵-methyl-N⁵-(3-sulfophenyl)-L-glutamine

Potassium carbonate (177 mg, 1.28 mmol), DMF (2 mL) and MeI (60 μL) were added to the compound (230 mg, 0.65 mmol) obtained in step 1, and stirred at 40° C. for 6 hours. Potassium carbonate (44.3 mg) and MeI (40 μL) were further added thereto and stirred overnight. After removing a solvent, purification was conducted in accordance with the purification process A to obtain a crude product (160 mg) of 3-{methyl[(2-nitrophenyl) sulfonyl]amino}benzenesulfonic acid. The crude product (144 mg, 0.39 mml) was dissolved in DMF (3 mL), and cesium carbonate (126 mg, 0.39 mmol) and thiophenol (40 μL, 0.39 mmol) were added thereto and stirred at 50° C. overnight. After removing a solvent, purification was conducted in accordance with the purification process A to obtain to a crude product (84.1 mg) of 3-(methylamino)benzenesulfonic acid. Then, a title compound was obtained by the same method as that of the synthetic example 1 except that the crude product of 3-(methylamino)benzenesulfonic acid was used instead of 3-sulfoaniline.

Yield amount: 5.14 mg

ESI (m/z): 317 [M+H]+

Synthetic Example 13 Synthesis of O-{[(3-sulfophenyl)amino]carbonyl}-L-serine (Compound No. 13)

Boc-Ser-OtBu (200 mg, 0.77 mmol) was dissolved in 3 mL of methylene chloride and cooled down to 0° C. N,N′-carbonyldiimidazole (124 mg, 0.77 mmol) was added thereto and stirred at room temperature for 2 hours. After removing a solvent, 3-aminobenzenesulfonic acid (132.6 mg, 0.77 mmol), 2 mL of DMF and 0.4 mL of diisopropylethylamine were added thereto and stirred at 70° C. overnight. After removing a solvent, the mixture was purified in accordance with the purification process A to obtain an intermediate. The obtained intermediate was dissolved in 1 mL of TFA and stirred at room temperature for 2 hours. After removing a solvent, purification was conducted in accordance with the purification process A to obtain a title compound.

Yield amount: 1.39 mg yield: 0.6%

ESI (m/z): 304 [M+H]+

Synthetic Example 14 Synthesis of 3-(L-γ-glutamylamino)benzoic acid (Compound No. 14)

Boc-Glu-OtBu (100 mg, 0.33 mmol) and HATU (150.4 mg, 0.40 mmol) were dissolved in 2 mL of DMF. Triethylamine (68.5 μL) was added thereto and stirred for 10 minutes. Ethyl 3-aminobenzoate (49.2 mg, 0.33 mmol) was added thereto and stirred overnight. After liquid separation was conducted with an ethyl acetate and an aqueous solution of 1M sodium hydroxide, the organic layer was washed with an aqueous solution of 1M sodium hydroxide, 1M hydrochloric acid and a saturated saline solution, successively, and dried with sodium sulfate to remove a solvent. The obtained residue was dissolved in 2 mL of THF, 1 mL of ethanol and 1 mL of water, and lithium hydroxide monohydrate (13.5 mg, 0.32 mmol) was added thereto. After stirring the mixture for 5 hours, 4.5 mg of lithium hydroxide was added thereto and stirred overnight. After confirming the completion of the reaction, pH of the reaction solution was adjusted to 2 with 1M hydrochloric acid, and a solvent was removed therefrom. 3 mL of TFA was added to the obtained residue and stirred at room temperature for 5 hours. After removing a solvent, purification was conducted in accordance with the purification process A to obtain a title compound.

Yield amount: 54.17 mg yield: 61%

1H-NMR (D2O, 300 MHz): δ 7.92 (s, 1H), 7.72 (d, 1H, J=7.5 Hz), 7.55 (d, 1H, J=9 Hz), 7.42 (dd, 1H, J=7.5, 9.0 Hz), 4.00-3.80 (m, 1H), 2.58-2.54 (m, 2H), 2.20-2.15 (m, 2H)

ESI (m/z): 267 [M+H]+

Synthetic Example 15 Synthesis of 3-(L-γ-glutamylamino)-2-hydroxybenzoic acid (Compound No. 15)

A title compound was obtained by the same method as that of the synthetic example 14 except that ethyl 3-amino-2-hydroxybenzoate was used instead of ethyl 3-aminobenzoate.

Yield amount: 34.1 mg yield: 37%

1H-NMR (D2O, 300 MHz): δ 7.70-7.60 (m, 2H), 6.87 (t, 1H), 3.91 (t, 1H), 2.63-2.55 (m, 2H), 2.20-2.10 (m, 2H)

ESI (m/z): 283 [M+H]+

Synthetic Example 16 Synthesis of 3-bromo-5-(L-γ-glutamylamino)benzoic acid (Compound No. 16)

A title compound was obtained by the same method as that of the synthetic example 14 except that methyl 3-amino-5-bromobenzoate was used instead of ethyl 3-aminobenzoate.

Yield amount: 16.8 mg

1H-NMR (D2O, 300 MHz): δ 7.80-7.85 (s*2, 2H), 3.75-3.90 (m, 1H), 2.45-2.55 (m, 2H), 2.10-2.20 (m, 2H)

ESI (m/z): 345, 347 [M+H]+

Synthetic Example 17 Synthesis of N⁵-{3-[hydroxyl(methoxy)phosphoryl]phenyl}-L-glutamine (Compound No. 17)

1-Iodo-3-nitrobenzene (249 mg, 1 mmol was dissolved in 10 mL of acetonitrile. Tetrakis(triphenylphosphine)palladium (58 mg, 3 mol %), dimethyl phosphite (0.138 ml, 1.5 mmol) and triethylamine (0.28 ml, 2 mmol) were added thereto and stirred at 70° C. overnight. After removing a solvent, the mixture was purified in accordance with the purification process A to obtain a mixture (0.222 g) of monomethyl (3-nitrophenyl)phosphonate and dimethyl ester. The obtained monomethyl phosphonate was dissolved in 10 mL of methanol. Pd/C in catalyst quantity was added thereto and stirred under hydrogen atmosphere overnight. After filtering out the catalyst, a solvent was removed to obtain a mixture of monomethyl(3-aminophenyl)phosphonate and dimethyl ester.

Boc-Glu-OtBu (303 mg, HOAt (136 mg, 1 mmol) and HATU (380 mg, 1 mmol) were dissolved in 1 mL of DMF, and triethylamine (0.278 ml) was added thereto. 10 minutes later, the mixture of monomethyl(3-aminophenyl)phosphonate and dimethyl ester was added thereto and stirred at room temperature overnight. After removing a solvent, purification was conducted in accordance with the purification process A to obtain a title compound.

Yield amount: 11.5 mg

1H-NMR (D2O, 300 MHz): δ 7.50-7.90 (m, 4H), 4.14-4.18 (m, 1H), 3.56 (s, 1.5H), 3.52 (s, 1.5H), 2.68-2.74 (m, 2H), 2.280-2.37 (m, 2H)

ESI (m/z): 317 [M+H]+

Synthetic Example 18 Synthesis of N⁵-(3-phosphonophenyl)-L-glutamine (Compound No. 18)

4 mL of DMF and trimethylsilyl bromide (1 mL) were added to the mixture (170 mg) of monomethyl(3-nitrophenyl)phosphonate and dimethyl ester, and stirred at 60° C. for 2 hours. After removing a solvent, the mixture was dissolved in a mixed solvent of water and methanol. Pd/C in catalyst quantity was added thereto and stirred under hydrogen atmosphere overnight. After filtering out the catalyst, a solvent was removed to obtain a crude product of (3-aminophenyl)phosphonic acid.

Boc-Glu-OtBu (236 mg, 0.78 mmol), HOAt (127 mg, 0.936 mmol) and HATU (356 mg, 0.936 mmol) were dissolved in 1 mL of DMF, and triethylamine (0.21 ml) was added thereto. 10 minutes later, the crude product of (3-aminophenyl)phosphonic acid was added thereto and stirred at room temperature overnight. After removing a solvent, purification was conducted in accordance with the purification process A to obtain a title compound.

Yield amount: 2.5 mg

ESI (m/z): 303 [M+H]+

Synthetic Example 19 Synthesis of N⁵-(3-nitrophenyl)-L-glutamine (Compound No. 19)

A title compound was obtained by the same method as that of the synthetic example 1 except that 3-nitroaniline was used instead of 3-sulfoaniline.

Yield amount: 61.6 mg yield: 93%

1H-NMR (DMSO-d6, 300 MHz): δ 10.5 (s, 1H), 8.66 (s, 1H), 7.86-7.93 (m, 2H), 7.61 (t, 1H, J=8.2 Hz), 3.99 (t, 1H, J=6.2 Hz), 2.50-2.70 (m, 2H), 2.06-2.16 (m, 2H) ESI (m/z): 268 [M+H]+

Synthetic Example 20 N-γ-glutamyl-aniline (Compound No. 20)

The product purchased from Bachem was used as the compound No. 20.

The following examples will further illustrate synthesis of the other representative compounds of the present invention shown in Table 2. They only explain the compounds of the present invention and do not particularly limit them.

TABLE 2 Comp. No. R₁ R₂ R₃ R₄ R₅ R₆ X 21 H SO₃H Me Cl H H CH₂ 22 H SO₃H H Cl Me H CH₂ 23 OH SO₃H H NO₂ H H CH₂ 24 Cl CO₂H H Cl H H CH₂ 25 Cl CO₂H H H H H CH₂ 26 H CO₂H H H Cl H CH₂ 27 OMe CO₂H H H H H CH₂ 28 H CO₂H OH H H H CH₂ 29 H CO₂H H H Me H CH₂ 30 H CO₂H H OH H H CH₂ 31 Me CO₂H H H H H CH₂ 32 H CO₂H H Cl H H CH₂ 33 H SO₃H Me Cl H H O 34 OH SO₃H H Cl H H O 35 H SO₃H H Cl Me H O 36 OMe SO₃H H Cl H H O 37 H SO₃H H H Cl H CH₂ 38 H H SO₃H Cl H H CH₂ 39 SO₃H H H Br H H CH₂ 40 H H SO₃H I H H CH₂ 41 SO₃H H H I H H CH₂ 42 H SO₃H H H H OH CH₂ 43 H SO₃H H H H OH O

Synthetic Example 21 Synthesis of N⁵-(3-chloro-4-methyl-5-sulfophenyl)-L-glutamine (Compound No. 21)

1 mL of Methylene chloride and 1 mL of THF were added to 303 mg (1 mmol) of Boc-Glu-OtBu hydrochloride and 180 mg (1.1 mmol) of CDI. 221 mg of 5-Amino-3-chloro-2-methylbenzenesulfonic acid was added thereof and stirred at room temperature overnight. Purification was conducted in accordance with the purification process A to obtain a protected form of the intended compound. The obtained protected form was dissolved in 5 mL of a trifluoroacetic acid and stirred for 2 hours. After removing a solvent, purification was conducted in accordance with the purification process A to obtain a title compound.

1H-NMR (D2O) δ: 7.71 (d, 1H), 7.60 (d, 1H), 3.93 (t, 1H), 2.50-2.57 (m, 2H), 2.47 (s, 3H), 2.10-2.20 (m, 2H)

ESI-MS: 349 [M−H]−, 351 [M+H]+

Synthetic Example 22 Synthesis of N⁵-(3-chloro-2-methyl-5-sulfophenyl)-L-glutamine (Compound No. 22)

2 mL of DMF and 0.52 mL (3 mmol) of DIEA were added to 303 mg (1 mmol) of Boc-Glu-OtBu hydrochloride, 221 mg (1 mmol) of 3-amino-5-chloro-4-methylbenzenesolfonic acid, 160 mg (1.3 mmol) of HOAt and 410 mg (1.3 mmol) of HATU, and stirred at room temperature overnight. The reaction solution was diluted with water-acetonitrile and purified in accordance with the purification process A to obtain a protected form of the intended compound. The obtained protected form was dissolved in 5 mL of a trifluoroacetic acid and stirred for 2 hours. After removing a solvent, purification was conducted in accordance with the purification process A to obtain a title compound.

Yield amount: 150 mg

1H-NMR (D2O) δ: 7.81 (d, 1H), 7.61 (d, 1H), 4.10 (t, 1H), 2.74-2.81 (m, 2H), 2.24-2.37 (m, 5H)

ESI-MS: 349 [M−H]−, 351 [M+H]+

Synthetic Example 23 Synthesis of N⁵-(2-hydroxy-5-nitro-3-sulfophenyl)-L-glutamine (Compound No. 23)

A title compound was obtained by the same method as that of the synthetic example 22 except that 3-amino-2-hydroxy-5-nitrobenzenesulfonic acid was used instead of 3-amino-5-chloro-4-methylbenzenesolfonic acid.

Yield amount: 185 mg

1H-NMR (D2O) δ: 8.55 (d, 1H, J=2.4 Hz), 8.29 (d, 1H, J=2.7 Hz), 3.95 (t, 1H, J=6.3 Hz), 2.66 (t, 2H, J=7.2 Hz), 2.10-2.30 (m, 2H)

ESI-MS: 362 [M−H]−, 364 [M+H]+

Synthetic Example 24 Synthesis of 2,5-dichloro-3-(L-γ-glutamylamino)benzoic acid (Compound No. 24) Step 1

206 mg (1.0 mmol) of 2,5-Dichloro-3-aminobenzoic acid was dissolved in 4 mL of acetone. 0.7 mL (1.4 mmol) of A hexane solution of 2.0M trimethylsilyldiazomethane was added thereto and stirred at room temperature for 1.5 hours. A solvent was removed to obtain methyl 2,5-dichloro-3-aminobenzoate.

Yield amount: 220 mg

Step 2

190 mg (0.5 mmol) of HATU, 70 mg (0.5 mmol) of HOAt, 152 mg (0.5 mmol) of Boc-Glu-OtBu hydrochloride, 0.21 mL (1.5 mmol) of triethylamine and 2 mL of dichloromethane were added to 110 mg (0.5 mmol) of methyl 2,5-dichloro-3-aminobenzoate, and stirred at room temperature overnight.

After removing a solvent, the mixture was extracted with ethyl acetate-water. The organic layer thereof was treated with a saturated saline solution and dried with sodium sulfate. After filtering out sodium sulfate and removing a solvent, 5 mL of 1N sodium hydroxide solution was added thereto and stirred at room temperature for 2 hours. Then, 5 mL of a trifluoroacetic acid was added thereto and stirred at room temperature for 2 hours. After removing a solvent, purification was conducted in accordance with the purification process A to obtain a title compound.

Yield amount: 6.6 mg

1H-NMR (CD3OD) δ: 8.08 (s, 1H), 7.56 (s, 1H), 3.95-4.01 (m, 1H), 2.76-2.82 (m, 2H), 2.20-2.30 (m, 2H)

ESI-MS: 333 [M−H]−, 335 [M+H]+

Synthetic Example 25 Synthesis of 2-chloro-3-(L-γ-glutamylamino)benzoic acid (Compound No. 25)

A title compound was obtained by the same method as that of the synthetic example 24 (synthesis of Compound No. 24) except that 2-chloro-3-aminobenzoic acid was used instead of the benzoic acid derivative.

Yield amount: 4.0 mg

1H-NMR (D2O) δ: 7.47-7.56 (m, 1H), 7.39-7.46 (m, 1H), 7.27-7.32 (s, 1H), 3.81-387 (m, 1H), 2.59-2.65 (m, 2H), 2.12-2.21 (m, 2H)

ESI-MS: 299 [M−H]−, 301 [M+H]+

Synthetic Example 26 Synthesis of 4-chloro-3-(L-γ-glutamylamino)benzoic acid (Compound No. 26)

A title compound was obtained by the same method as that of the synthetic example 24 (synthesis of Compound No. 24) except that 4-chloro-3-aminobenzoic acid was used instead of the benzoic acid derivative.

Yield amount: 5.3 mg

1H-NMR (D2O) δ: 8.03 (s, 1H), 7.76-7.79 (m, 1H), 7.52-7.55 (m, 1H), 3.78-3.84 (m, 1H), 2.59-2.65 (m, 2H), 2.12-2.22 (m, 2H)

ESI-MS: 299 [M−H]−, 301 [M+H]+

Synthetic Example 27 Synthesis of 2-methoxy-3-(L-γ-glutamylamino)benzoic acid (Compound No. 27)

84 mg (0.2 mmol) of HATU, 30 mg (0.2 mmol) of HOAt, 61 mg (0.2 mmol) of Boc-Glu-OtBu hydrochloride, 0.084 mL (0.6 mmol) of triethylamine and 1 mL of dichloromethane were added to 36 mg (0.2 mmol) of methyl 2-methoxy-3-aminobenzoate, and stirred at room temperature overnight.

After removing a solvent, the mixture was extracted with ethyl acetate-water. The organic layer thereof was treated with a saturated saline solution and dried with sodium sulfate. After filtering out sodium sulfate and removing a solvent, 5 mL of 1N sodium hydroxide solution was added thereto and stirred at room temperature for 2 hours. Then, 5 mL of a trifluoroacetic acid was added thereto and stirred at room temperature for 2 hours. After removing a solvent, purification was conducted in accordance with the purification process A to obtain a title compound.

Yield amount: 6.5 mg

1H-NMR (D2O) δ: 7.69-7.71 (m, 1H), 7.56-7.59 (m, 1H), 7.13-7.18 (m, 1H), 3.87-3.93 (m, 1H), 3.68 (s, 3H), 2.60-2.66 (m, 2H), 2.12-2.22 (m, 2H)

ESI-MS: 295 [M−H]−, 297 [M+H]+

Synthetic Example 28 Synthesis of 6-hydroxy-3-(L-γ-glutamylamino)benzoic acid (Compound No. 28)

6-methoxy-3-(L-γ-glutamylamino)benzoic acid was synthesized by the same method as that of the synthetic example 27 (synthesis of Compound No. 27) except that 6-methoxy-3-aminobenzoic acid was used instead of the benzoic acid derivative. Then, purification was conducted in accordance with the purification process A to obtain a title compound that is obtained as a by-product in the synthetic process.

Yield amount: 2.1 mg

ESI-MS: 280 [M−H]−, 282 [M+H]+

Synthetic Example 29 Synthesis of 4-methyl-3-(L-γ-glutamylamino)benzoic acid (Compound No. 29)

500 mg of 4-Methyl-3-nitrobenzoic acid was dissolved in 5 mL of methanol and 10 mL of a dioxane solution containing 4N hydrogen chloride. After stirring the mixture at room temperature for 2 days, a solvent was removed to obtain a crude product. The obtained crude product was dissolved in 10 mL of methanol, and Pd/C in catalyst quantity was acted thereon under hydrogen atmosphere at room temperature overnight. After filtering out the catalyst, a solvent was removed to obtain a crude product. 165 mg of the obtained crude product, 303 mg (1 mmol) of Boc-Glu-OtBu hydrochloride and 400 mg (about 1.3 mmol) of HATU were dissolved in 1 mL of DMF. 0.26 mL of DIEA was added thereto and stirred overnight. The reaction solution was diluted with water-acetonitrile and purified in accordance with the purification process A to obtain 0.31 g of a protected form of the intended compound. 3 mL of THF, 1.5 mL of methanol and 1.5 mL of water were added to the obtained protected form, and then 26 mg (0.82 mmol) of lithium hydroxide monohydrate was further added thereto. After stirring the mixture for 2 hours, a solvent was removed. 3 mL of THF, 1.5 mL of methanol and 1.5 mL of water were again added thereto, then 26 mg (0.82 mmol) of lithium hydroxide monohydrate was further added thereto and stirred for 2 hours. After adding 2 mL of ethyl acetate thereto, a solvent was removed. Then, 3 mL of a trifluoroacetic acid was added thereto and stirred at room temperature for 2 hours. After removing a solvent, purification was conducted in accordance with the purification process A to obtain a title compound.

1H-NMR (D2O) δ: 7.74-7.77 (m, 1H), 7.30-7.36 (m, 1H), 3.75-3.81 (m, 1H), 2.55-2.62 (m, 2H), 2.10-2.20 (m, 5H)

ESI-MS: 279 [M−H]−, 281 [M+H]+

Synthetic Example 30 Synthesis of 5-hydroxy-3-(L-γ-glutamylamino)benzoic acid (Compound No. 30)

5-methoxy-3-(L-γ-glutamylamino)benzoic acid was synthesized by the same method as that of the synthetic example 27 (synthesis of Compound No. 27) except that 5-methoxy-3-aminobenzoic acid was used instead of the benzoic acid derivative. Then, purification was conducted in accordance with the purification process A to obtain a title compound that is obtained as a by-product in the synthetic process.

Yield amount: 7.5 mg

ESI-MS: 280 [M−H]−, 282 [M+H]+

Synthetic Example 31 Synthesis of 3-(L-γ-glutamylamino)-2-methyl-benzoic acid (Compound No. 31)

A title compound was obtained by the same method as that of the synthetic example 29 (synthesis of Compound No. 29) except that 2-methyl-3-nitrobenzoic acid was used instead of the benzoic acid derivative.

Yield amount: 37 mg

1H-NMR (D2O) δ: 7.56 (dd, 1H), 7.30 (dd, 1H), 7.23 (t, 1H), 3.82 (t, 1H), 2.5-2.62 (m, 2H), 2.21 (s, 3H), 2.10-2.29 (m, 2H)

ESI-MS: 279 [M−H]−, 281 [M+H]+

Synthetic Example 32 Synthesis of 5-chloro-3-(L-γ-glutamylamino)benzoic acid (Compound No. 32) Step 1

8 mL of methanol and 2 mL of THF were added to 228 mg (1 mmol) of methyl 5-chloro-1,3-dibenzoate and 56 mg (1 mmol) of potassium hydroxide, and stirred at room temperature overnight. The reaction solution was concentrated under reduced pressure. 4 mL of Toluene, 0.12 mL (0.85 mmol) of triethylamine and 0.19 mL (0.88 mmol) of diphenylphosphoryl azide were added thereto and stirred at 50° C. for 1 hour. Then, 0.19 mL (2 mmol) of t-butyl alcohol and 2 mL of toluene were added thereto and stirred at 80° C. overnight. After cooling the mixture down to room temperature, it was extracted with ethyl acetate-water. The organic layer thereof was treated with a saturated saline solution and dried with sodium sulfate. After filtering out sodium sulfate and removing a solvent, purification was conducted in accordance with the purification process A to obtain methyl 5-chloro-3-aminobenzoate-trifluoroacetate.

Yield amount: 30 mg

Step 2

38 mg (0.1 mmol) of HATU, 14 mg (0.1 mmol) of HOAt, 30 mg (0.1 mmol) of Boc-Glu-OtBu hydrochloride, 0.014 mL (0.1 mmol) of triethylamine and 1 mL of dichloromethane were added to 30 mg (0.1 mmol) of methyl 5-chloro-3-aminobenzoate, and stirred at room temperature overnight.

After removing a solvent, the mixture was extracted with ethyl acetate-water. The organic layer thereof was treated with a saturated saline solution and dried with sodium sulfate. After filtering out sodium sulfate and removing a solvent, 5 mL of 1N sodium hydroxide solution was added thereto and stirred at room temperature for 2 hours. Then, 5 mL of a trifluoroacetic acid was added thereto and stirred at room temperature for 2 hours. After removing a solvent, purification was conducted in accordance with the purification process A to obtain a title compound.

Yield amount: 1.0 mg

1H-NMR (D2O) δ: 7.54 (s, 1H), 7.48 (s, 1H), 7.45 (s, 1H), 3.96-4.00 (m, 1H), 2.50-2.56 (m, 2H), 2.12-2.20 (m, 2H)

ESI-MS: 301 [M−H]−, 301 [M+H]+

Synthetic Example 33 Synthesis of O-{[(3-chloro-4-methyll-5-sulfophenyl)amino]carbonyl}-L-serine (Compound No. 33)

100 mg (0.38 mmol) of Boc-Ser-OtBu, 86 mg (0.38 mmol) of 5-amino-3-chloro-2-methylbenzenesulfonic acid and 37 mg (0.0127 mmol) of triphosgene were suspended in 1 mL of methylene chloride, and 66 μL (0.76 mmol) of DIEA was added thereto. After stirring the mixture at room temperature overnight, a solvent was removed. Purification was conducted in accordance with the purification process A to obtain a protected form of a title compound. The obtained protected form was dissolved in 2 mL of a trifluoroacetic acid and stirred for 2 hours. After removing a solvent, purification was conducted in accordance with the purification process A to obtain a title compound.

Yield amount: 15.5 mg

1H-NMR (D2O) δ: 7.67 (d, 1H), 7.57. (d, 1H), 4.51 (t, 2H), 4.15 (dd, 1H) 2.47 (s, 3H)

ESI-MS: 351 [M−H]−, 353 [M+H]+

Synthetic Example 34 Synthesis of sodium 3-{[(2S)-2-amino-2-carboxyethoxycarbonyl]amino}-5-chloro-2-hydroxybenzenesulfonate (Compound No. 34)

The same method was used as that of the synthetic example 33 (synthesis of Compound No. 33) except that 3-amino-5-chloro-2-hydroxybenzenesulfonic acid was used instead of the benzenesulfonic acid derivative. Then, 1 equivalent of an aqueous solution of 0.1N sodium hydroxide was added thereto and freeze-dried to obtain a title compound.

Yield amount: 15.1 mg

1H-NMR (D2O) δ: 7.70 (s, 1H), 7.37 (d, 1H, J=2.6 Hz), 4.37-4.55 (m, 2H), 3.98 (dd, 1H, J=3.0, 5.3 Hz),

ESI-MS: 353 [M−H]−, 355 [M+H]+

Synthetic Example 35 Synthesis of O-{[(3-chloro-2-methyl-5-sulfophenyl)amino]carbonyl}-L-serine (Compound No. 35)

A title compound was obtained by the same method as that of the synthetic example 33 (synthesis of Compound No. 33) except that 3-amino-5-chloro-4-methylbenzenesulfonic acid was used instead of the benzenesulfonic acid derivative.

Yield amount: 3.9 mg

1H-NMR (D2O) δ: 7.60-7.64 (m, 2H), 4.42-4.54 (m, 2H), 4.03 (dd, 1H, J=3.2, 4.8 Hz)

ESI-MS: 351 [M−H]−, 353 [M+H]+

Synthetic Example 36 Synthesis of O-{[(5-chloro-2-methoxy-3-sulfophenyl)amino]carbonyl}-L-serine (Compound No. 36)

2 mL of acetone was added to 30 mg of a protected form obtained in the synthetic example 34 (synthesis of Compound No. 34. 1 mL of A hexane solution containing 2M trimethylsilyldiazomethane and 100 μL of triethylamine were further added thereto. After stirring the mixture for 20 minutes, a solvent was removed. Then, the mixture was purified in accordance with the purification process A to obtain a methylated form. The obtained methylated form was dissolved in 2 mL of a trifluoroacetic acid and stirred at room temperature for 3 hours. After removing a solvent, water was added thereto and freeze-dried to obtain a title compound.

Yield amount: 1.48 mg

1H-NMR (D2O) δ: 7.64 (brs, 1H), 7.27 (d, 1H, J=2.6 Hz), 4.25-4.22 (m, 2H), 3.80 (dd, 1H, J=3.1, 5.0 Hz), 3.52 (s, 3H)

Synthetic Example 37 Synthesis of N⁵-(2-chloro-5-sulfophenyl)-L-glutamine (Compound No. 37)

2 mL of methanol and 3 mL of water were added to sodium 4-chloro-3-nitrobenzenesulfonate (1 mmol). 2% Pt-S/C in catalyst quantity was added thereto and stirred under hydrogen atmosphere overnight at room temperature. After filtering out the catalyst, the mixture was sufficiently dried. Then, 303 mg (1 mmol) of Boc-Glu-OtBu hydrochloride, 163 mg (1.2 mmol) of HOAt, 456 mg (1.2 mmol) of HATU, 2 mL of DMF and 0.35 mL of DIEA were added thereto and stirred at room temperature overnight. The reaction solution was diluted with water-acetonitrile and purified in accordance with the purification process A to obtain a protected form of a title compound. The obtained protected form was dissolved in 3 mL of a trifluoroacetic acid and stirred at room temperature for 2 hours. After removing a solvent, purification was conducted in accordance with the purification process A to obtain a title compound.

Yield amount: 69.9 mg

1H-NMR (D2O) δ: 7.85 (brs, 1H), 7.50-7.55 (m, 2H), 4.03 (t, 1H), 2.66 (t, 2H, J=7.1 Hz), 2.10-2.30 (m, 2H)

ESI-MS: 335 [M−H]−, 337 [M+H]+

Synthetic Example 38 Synthesis of N⁵-(3-chloro-4-sulfophenyl)-L-glutamine (Compound No. 38) Step 1

0.4 mL of 3-chloroaniline was slowly added to 4 mL of a fuming sulfuric acid and stirred at room temperature overnight. Cooling it down to 0° C., the reaction solution was poured in water, and a precipitated solid substance was taken by filtration. The solid substance was dissolved in an aqueous solution of 2N sodium hydroxide. Then, a concentrated hydrochloric acid wad added thereto to make the liquid acidic. The precipitated solid substance was filtered out to obtain a crude product of 4-amino-2-chlorobenzenesulfonic acid.

Yield amount: 80 mg

Step 2

A title compound was obtained by the same method as that of the synthetic example 21 (synthesis of Compound No. 21) except that the crude product of 4-amino-2-chlorobenzenesulfonic acid obtained in the step 1 was used instead of the benzenesulfonic acid derivative.

Yield amount: 40 mg

1H-NMR (D2O) δ: 7.80 (d, 1H), 7.63 (d, 1H), 7.33 (dd, 1H), 3.94 (t, 1H), 2.50-2.60 (m, 2H), 2.10-2.22 (m, 2H)

ESI-MS: 337 [M+H]+, 335 [M−H]−

Synthetic Example 39 Synthesis of N⁵-(5-bromo-2-sulfophenyl)-L-glutamine (Compound No. 39)

A title compound was obtained by the same steps as those of the synthetic example 38 (synthesis of Compound No. 38) except that 3-bromoaniline was used instead of the aniline derivative used in the step 1 of the example 38.

Yield amount: 9.9 mg

ESI-MS: 429 [M+H]+, 427 [M−H]−

Synthetic Example 40 Synthesis of N⁵-(3-iodo-4-sulfophenyl)-L-glutamine (Compound No. 40)

A title compound was obtained by the same steps as those of the synthetic example 38 (synthesis of Compound No. 38) except that 3-iodoaniline was used instead of the aniline derivative used in the step 1 of the example 18.

Yield amount:

1H-NMR (D2O) δ: 8.12 (s, 1H), 7.84 (d, 1H), 7.44 (dd, 1H), 3.75-3.90 (m, 1H), 2.50-2.60 (m, 2H), 2.00-2.20 (m, 2H)

ESI-MS: 429 [M+H]+, 427 [M−H]−

Synthetic Example 41 Synthesis of N⁵-(5-iodo-2-sulfophenyl)-L-glutamine (Compound No. 41)

This compound was obtained as a regioisomer in the synthetic example 40.

Yield amount:

1H-NMR (D2O) δ: 8.11 (d, 1H), 7.63-7.66 (m, 1H), 7.48 (d, 1H), 3.80-3.90 (m, 1H), 2.58-2.66 (m, 2H), 2.10-2.24 (m, 2H)

ESI-MS: 429 [M+H]+, 427 [M−H]−

Synthetic Example 42 Synthesis of N⁵-hydroxy-N⁵-(3-sulfophenyl)-L-glutamine (Compound No. 42)

270 mg (4.3 mmol) of zinc powder and 106 mg (2 mmol) of ammonium chloride were suspended in 2 mL of a mixed solvent of methanol:water=1:1. 450 mg (2 mmol) of sodium 2-nitrobenzenesulfonate was slowly added thereto. After heating the mixture up to 65° C. and stirring it for 1 hour, an insoluble substance was filtered, and the obtained filtrate was removed to obtain a crude product of a hydroxylamine derivative. 5 mL of DMF and 0.35 mL of DIEA were added to 450 mg (1.5 mmol) of Boc-Glu-OtBu hydrochloride, 230 mg (1.7 mmol) of HOAt and 646 mg (1.7 mmol) of HATU, and stirred for 10 minutes. Then, the solution was added to the obtained crude product and stirred overnight. Purification was conducted in accordance with the purification process A to obtain a protected form of a title compound. 4 mL of TFA was added to the obtained protected form and stirred for 2 hours. After removing TFA, purification was conducted in accordance with the purification process A to obtain a title compound.

Yield amount: 135 mg

1H-NMR (DMSO) δ: 10.65 (s, 1H), 10.04 (s, 1H), 7.20-8.40 (m, 7H), 3.90-4.10 (m, 1H), 2.60-3.00 (m, 2H), 1.90-2.20 (m, 2H)

ESI-MS: 317 [M−H]−, 319 [M+H]+

Synthetic Example 43 Synthesis of O-{[hydroxy(3-sulfophenyl)amino]carbonyl}-L-serine (Compound No. 43)

2 mL of Methylene chloride and 0.35 mL of DIEA were added to Boc-Ser-OtBu (1 mmol), the crude product of hydroxylamine obtained in synthetic example 42 and 100 mg (0.33 mmol) of triphosgene, and stirred at room temperature overnight. After removing a solvent, the obtained residue was purified in accordance with the purification process A to obtain a protected form of a title compound. The obtained protected form was dissolved in 4 mL of TFA and stirred at room temperature for 3 hours. After removing TFA, purification was conducted in accordance with the purification process A to obtain a title compound.

Yield amount: 6.6 mg

1H-NMR (D2O) δ: 7.78-7.80 (m, 1H), 7.43-7.60 (m, 4H), 4.56-4.58 (m, 2H), 4.10-4.15 (m, 1H)

ESI-MS: 319 [M−H]−, 321 [M+H]+

Example II Preparation of a CaSR Gene

A CaSR gene was prepared as follows. Based on the DNA sequence registered in NCBI (CaSR (calcium receptor): NM_(—)000388, Seq. Nos. 1-2), synthetic oligo DNA used in PCR was synthesized (forward primer (Seq. No. 3:ACTAATACGACTCACTATAGGGACCATGGCATTTTATAGCTGCTGCTGG) and reverse primer (Seq. No. 4: TTATGAATTCACTACGTTTTCTGTAACAG).

PCR was conducted under following conditions by using as a material cDNA derived from human kidney (by Clontech) and also using the above primers and Pfu Ultra DNA Polymerase (by Stratagene). The reactions at 94° C. for 3 minutes, at 94° C. for 30 seconds, at 55° C. for 30 seconds and at 72° C. for 2 minutes were repeated 35 times, and the reaction at 72° C. for 7 minutes was conducted. Agarose electrophoresis was conducted to confirm whether the intended product was amplified by PCR, and the product was dyed in DNA dyeing test and then detected with ultraviolet irradiation. At the same time, a chain length of the PCR product was confirmed by comparing it with a DNA marker to which electrophoresis was conducted and of which size is known. Plasmid vector pBr322 was cut by restriction enzyme EcoRV (by Takara). The gene fragment amplified by PCR was connected with Ligation kit (by Promega) to the cut part. E. coli DH5α was transformed in the reaction solution, and the transformant holding a plasmid cloning the product amplified by PCR was selected. It was confirmed by DNA sequence analysis that the product amplified by PCR comprises a CaSR gene. Plasmid expressing human CaSR: hCaSR/pcDNA3.1 was prepared by using this recombinant plasmid.

Example III Evaluation of CaSR Agonistic Activity

(Method of Evaluating a CaSR Agonist)

293E cells (HEK293 cell expressing EBNA1, ATCC No. CRL-10852) were cultured in DMEM containing 10% fetal bovine serum (Dulbecco's modified Eagle medium containing 1.0 g/mL Glucose, by NACALAI TESQUE, INC.), in the presence of 250 μg/mL of G418. The cells were spread on a petri dish of 10 cm diameter in 1.8×10⁶ cells/15 mL. After leaving them in the CO₂ incubator (5% CO₂, 37° C.) for 24 hours, plasmid expressing human CaSR: hCaSR/pcDNA3.1 was transfected with a transfection reagent: Mirus TransIT 293 (by Takara Bio Inc.). After leaving it in the CO₂ incubator for 24 hours, the cells were collected by DMEM containing 10% fetal bovine serum and seeded on poly-D-lysine coat 384 well plate (by Falcon) in 15,000 cells/well. After leaving them in the CO₂ incubator for 24 hours, the medium was removed. Then, 50 μL/well of Ca²⁺ fluorescent indicator: Calcium 4 Assay Kit (by Molecular Devices) that was dissolved in an assay buffer (146 mM NaCl, 5 mM KCl, 1 mM MgSO₄, 1 mg/mL Glucose, 20 mM HEPES (pH 7.2), 1.5 mM CaCl₂) was added thereto, and left at 37° C. for 1 hour and at room temperature for 30 minutes to absorb the fluorescent indicator. The 384 well plate was transferred to FLIPR (by Molecular Devices). Then, 12.5 μL/well of a compound that was dissolved in a 0.1% BSA containing assay buffer was added thereto, and change in fluorescence intensity was measured for 3 minutes. Meanwhile, Compound No. 20 was purchased from Bachem.

(Method of Calculating EC₅₀)

The difference between the maximum value and the minimum value (RFU(Max−Min)) of the fluorescence intensity before and after adding a compound was automatically calculated by FLIPR. RFU(Max−Min) when adding a compound in maximum concentration was defined as 100%; and RFU(Max−Min) when adding DMSO instead of the compound in the same concentration as that of the compound was defined as 0%. Based on them, activation rate was calculated, and curve-fitting was conducted by spreadsheet Xfit to calculate EC₅₀ that is a concentration of the compound having activation rate 50%. Tables 3 and 4 show the results of the compounds shown in Tables 1 and 2.

TABLE 3 Comp. No. EC₅₀ [μM] 1 0.012 2 2.3 3 0.56 4 0.059 5 0.13 6 2.7 7 0.0019 8 0.10 9 0.27 10 0.017 11 0.086 12 0.20 13 0.072 14 2.0 15 0.034 16 0.048 17 2.0 18 0.53 19 0.40 20 0.94

TABLE 4 Comp. No. EC₅₀ [μM] 21 0.0057 22 0.0014 23 0.89 24 0.022 25 0.97 26 0.16 27 0.15 28 0.33 29 0.53 30 2.9 31 3.7 32 0.0088 33 0.0021 34 0.0019 35 0.0037 36 3.5 37 0.0029 38 6.7 39 5.0 40 7.9 41 2.3 42 0.031 43 0.043

Example IV Effect of a CaSR Agonist on Water Absorption in Rat Large Intestine Loop Method (1)

(Method)

The cecum and large intestine were taken out from the abdomen of a male SD (IGS) rat under pentobarbital anesthesia, and a large intestine loop was prepared by ligating a part 5 cm just below the cecum. Immediately after preparing the loop, PGE2 (4 μg/mL/kg, SIGMA) was intraperitoneally administered. 30 minutes later, 2 mL of Tyrode solution (NaCl 136.9 mM, KCl 2.7 mM, CaCl₂.2H₂O 1.8 mM, MgCl₂.6H₂O 1.04 mM, NaH₂PO₄.2H₂O 0.04 mM, glucose 5.55 mM, NaHCO₃ 11.9 mM) was poured in the prepared loop. 1 hour later, the weight of the loop, the weight thereof when the liquid was removed from the loop, and the loop area were measured to calculate the weight per unit area of the liquid that remains in the loop.

A test compound was tested by dissolving it in Tyrode solution that was adjusted to pH 6.5 to 7.5.

The remaining liquid weight per unit area (g/cm²) was calculated by the following formula. Remaining liquid weight per unit area (g/cm²)=(loop weight−loop weight when the liquid was removed from the loop)/loop area

Water absorption was evaluated by calculating the inhibition ratio by the following formula. Inhibition ration (%)=100−(remaining liquid weight per unit area with a drug−basic average remaining liquid weight per unit area)/(average remaining liquid weight per unit area of vehicle−basic average remaining liquid weight per unit area)×100

The results are shown in FIG. 1. The water absorption of the compound No. 1 in Table 1 was promoted in a dose-dependent manner, and thus, it was indicated that the compound is useful as a therapeutic or preventive agent for diarrhea.

Example V Effect of a CaSR Agonist on Water Absorption in Rat Large Intestine Loop Method (2)

The same test was conducted on a compound No. 7 as the method of Example IV. The results are shown in FIG. 2. The water absorption of the compound No. 7 in Table 1 was promoted in a dose-dependent manner, and thus, it was indicated that the compound is useful as a therapeutic or preventive agent for diarrhea.

Example VI (Test Example 1) Evaluation of “Kokumi” Taste

<Kokumi-Imparting Activities of Compounds (Sodium Salts of Compound Nos. 1 and 7) Used in the Present Invention>

On compounds wherein a calcium receptor activating action was found (sodium salts of Compound Nos. 1, 7 and 21), the intensity of kokumi-imparting activity was examined by a quantitative sensory evaluation test. The used compound was prepared by dissolving 525 mg of the compound No. 1 described in Synthetic Example 1 of Example I in 5 mL of distilled water, adjusting it to pH6.5 to 7 by adding 16.4 mL of 0.1M sodium hydroxide solution thereto, and freeze-drying it to obtain a sodium salt thereof. Further, the used compound was also prepared as follows. 500 mg of the compound No. 7 described in Synthetic Example 7 of Example I was suspended in 5 mL of distilled water. 1.61 mL of 1M sodium hydroxide and 0.8 mL of 2M hydrochloric acid were added thereto at 0° C. respectively to precipitate a solid substance. The precipitated solid substance was taken by filtration and dried under reduced pressure at 40° C. to obtain 426 mg of the compound No. 7. The obtained solid substance was suspended in 10 mL of distilled water. 1.2 mL of 1M sodium hydroxide was added thereto and freeze-dried to obtain a sodium salt thereof. The compound No. 21 was used in the form of a sodium salt of the compound No. 21 described in Synthetic Example 21 of Example I, which was prepared by the same method as mentioned above.

A quantitative sensory evaluation test was conducted as follows. 0.000001 to 0.1 g/dL of the compound(s) (a sodium salt of No. 1) was mixed as a sample to distilled water containing glutamic sodium (0.05 g/dL), inosine monophosphate (0.05 g/dL) and sodium chloride (0.5 g/dL). Then, the intensity of kokumi-imparting activity was examined at that time. As a reference, γ Glu-Cys-Gly and γ Glu-Val-Gly were used, each of which is a known kokumi-imparting component. As for a sample that becomes acidic to an additive-free control after dissolving the sample, it was used by being adjusted with sodium hydroxide to become within pH±0.2 to the additive-free control. As for sensory scoring, it was defined as a control: 0, strong: 3, and very strong: 5; and n=4. Meanwhile, “first-middle taste” means the taste combining first taste and middle taste. The kokumi-imparting activity was widely seen in the above addition concentrations, and the results of the representative concentrations are shown in Table 5.

TABLE 5 Intensity of kokumi Conc. First-middle After Sample (g/dL) taste taste Comments Control — 0 0 — γGlu-Cys-Gly 0.01 3.0 3.0 Richness, thickness and continuity become stronger. γGlu-Val-Gly 0.001 2.5 3.0 Mellowness, richness and growth (mouthfullness) become mainly stronger. 0.005 3.5 4.0 Mellowness, richness and growth (mouthfullness) become mainly stronger. No.1-Na salt 0.00001 0.7 1.0 Though there is thickness, it is not enough. 0.0001 1.8 2.0 There is a harmony and a bit of thickness. 0.0005 2.6 3.0 There is a harmony, richness and thickness. 0.001 3.2 3.6 All tastes are strong, mainly thickness and continuity. 0.01 5.0 5.0 All tastes are strong. No.7-Na salt 0.00005 2.2 2.5 Thickness is felt mainly in the middle taste. 0.0001 2.5 3.2 There is about the same thickness as that of 0.001 γGlu-Val-Gly. 0.0005 3.3 4.0 Strong thickness is felt from the middle taste. It has a strong after taste. No.21-Na salt 0.0002 1.5 2.0 Richness is somewhat felt, but weak. 0.0005 2.6 3.1 Richness is felt. Umami and sweetness become stronger. 0.001 3.1 3.7 Though richness is strong, there is some bitterness and tastes are vague. 

What is claimed is:
 1. A compound of formula (I) or a pharmaceutically acceptable salt thereof:

wherein R1, R3, and R5 are each independently selected from the group consisting of a hydrogen atom, a halogen atom, a hydroxyl group, —NH₂, an optionally substituted alkyl group having 1 to 6 carbon atoms, and an optionally substituted alkoxy group having 1 to 6 carbon atoms; R4 is selected from the group consisting of a halogen atom, a hydroxyl group, —NH₂, and an optionally substituted alkoxy group having 1 to 6 carbon atoms; R2 is selected from the group consisting of a sulfonic acid group,

R6 and R₇ are each independently a hydrogen atom or an optionally substituted alkyl group having 1 to 6 carbon atoms; and X is a methylene group or an oxygen atom; and excluding a compound wherein X is a methylene group, and R2 is


2. The compound or pharmaceutically acceptable salt thereof according to claim 1, wherein R1, R3, and R5 are each independently selected from the group consisting of a hydrogen atom, a halogen atom, a hydroxyl group, —NH₂, an optionally substituted alkyl group having 1 to 3 carbon atoms, and an optionally substituted alkoxy group having 1 to 3 carbon atoms; R2 is selected from the group consisting of a sulfonic acid group,

and R6 and R₇ are each independently a hydrogen atom or a methyl group.
 3. The compound or pharmaceutically acceptable salt thereof according to claim 1, wherein R1, R3, and R5 are each independently selected from the group consisting of a hydrogen atom, a a chlorine atom, a bromine atom, a hydroxyl group, —NH₂, a methyl group, and a methoxy group; R2 is selected from the group consisting of a sulfonic acid group,

R6 is a hydrogen atom or a methyl group; R₇ is a hydrogen atom; and X is a methylene group.
 4. The compound or pharmaceutically acceptable salt thereof according to claim 1, wherein R2 is a sulfonic acid group, a carboxylic acid group, or a phosphonic acid group.
 5. A compound of formula (I) or a pharmaceutically acceptable salt thereof:

wherein R2 and R5 are each independently selected from the group consisting of a hydrogen atom, a halogen atom, a hydroxyl group, —NH₂, an optionally substituted alkyl group having 1 to 6 carbon atoms, and an optionally substituted alkoxy group having 1 to 6 carbon atoms; R4 is selected from the group consisting of a halogen atom, a hydroxyl group, —NH₂, and an optionally substituted alkoxy group having 1 to 6 carbon atoms; either of R1 or R3 is a sulfonic acid group and the other is selected from the group consisting of a hydrogen atom, a halogen atom, a hydroxyl group, an unsubstituted amino group, an optionally substituted alkyl group having 1 to 6 carbon atoms, and an optionally substituted alkoxy group having 1 to 6 carbon atoms; R6 is a hydrogen atom or an optionally substituted alkyl group having 1 to 6 carbon atoms; and X is a methylene group or an oxygen atom.
 6. The compound or pharmaceutically acceptable salt thereof according to claim 5, wherein R4 is a halogen atom.
 7. A pharmaceutical composition comprising the compound or pharmaceutically acceptable salt thereof according to claim
 1. 8. A pharmaceutical composition comprising the compound or pharmaceutically acceptable salt thereof according to claim
 5. 9. The compound or pharmaceutically acceptable salt thereof of claim 1, which is N⁵-(5-chloro-2-hydroxy-3-sulfophenyl)-L-glutamine.
 10. The compound or pharmaceutically acceptable salt thereof of claim 1, wherein X is methylene.
 11. A compound or pharmaceutically acceptable salt thereof, which is N⁵-(5-chloro-2-hydroxy-3-sulfophenyl)-L-glutamine, N⁵-(2-hydroxy-3-sulfophenyl)-L-glutamine, 3-(L-(-glutamylamino)-2-hydroxybenzoic acid, 3-bromo-5-(L-(-glutamylamino)benzoic acid, N⁵-(3-phosphonophenyl)-L-glutamine, N⁵-(3-chloro-4-methyl-5-sulfophenyl)-L-glutamine, 5-chloro-3-(L-(-glutamylamino)benzoic acid, O-{[(3-chloro-4-methyl-5-sulfophenyl)amino]carbonyl}-L-serine, 3-{[(2S)-2-amino-2-carboxyethoxycarbonyl]amino}-5-chloro-2-hydroxybenzensulfonic acid, or O-{[(3-chloro-2-methyl-5-sulfophenyl)amino]carbonyl}-L-serine.
 12. The compound or pharmaceutically acceptable salt thereof of claim 1, wherein X is an oxygen atom.
 13. The compound or pharmaceutically acceptable salt thereof of claim 1, which is O-{[(3-chloro-4-methyl-5-sulfophenyl)amino]carbonyl}-L-serine, 3-{[(2S)-2-amino-2-carboxyethoxycarbonyl]amino}-5-chloro-2-hydroxybenzensulfonic acid, or O-{[(3-chloro-2-methyl-5-sulfophenyl)amino]carbonyl}-L-serine.
 14. The compound or pharmaceutically acceptable salt thereof of claim 11, which is 3-(L-(-glutamylamino)-2-hydroxybenzoic acid, 3-bromo-5-(L-(-glutamylamino)benzoic acid, N⁵-(3-phosphonophenyl)-L-glutamine, or 5-chloro-3-(L-(-glutamylamino)benzoic acid.
 15. The compound or pharmaceutically acceptable salt thereof according to claim 1, wherein R4 is a halogen atom. 